In a large saucepan, melt margarine. Stir in flour and 1/4 teaspoon salt until smooth. Gradually add milk. Bring to a boil; cook and stir until thickened, 1-2 minutes. Remove from the heat. , Stir a small amount of sauce into egg yolk; return all to the pan, stirring constantly. Bring to a gentle boil; cook and stir for 2 minutes. Remove from the heat; stir in lemon juice and zest. Set aside and keep warm., Place spinach in a steamer basket. Sprinkle with pepper and remaining salt. Place in a saucepan over 1 in. of water. Bring to a boil; cover and steam until wilted and tender, 3-4 minutes., Meanwhile, in a skillet or omelet pan with high sides, bring 2 to 3 in. water to a boil. Reduce heat; simmer gently. Break cold eggs, 1 at a time, into a custard cup or saucer. Holding the dish close to the surface of the simmering water, slip the eggs, 1 at a time, into the water. Cook, uncovered, until whites are completely set and yolks begin to thicken, 3-5 minutes. Lift out of the water with a slotted spoon., Place spinach on each muffin half; top with an egg. Spoon 3 tablespoons sauce over each egg. Sprinkle with paprika. Serve immediately.